Plainclothes transit cops eating lunch in a Times Square diner – agog as a dandily dressed Brooklyn man stuffed piles of cash from an ATM into a gym bag – ended up nabbing a key player in a $4 million international identity-theft ring.

What began as a hankering for grilled chicken could be the coffin nail for the ring that has ripped off countless consumers and banks.

Feds had been investigating the syndicate with little luck.

They knew people were stealing the bank and credit-card account information and PIN numbers of consumers from all over the United States and withdrawing money from their accounts.

They even had video of a guy using a swag card to withdraw money but couldn’t ID him.

But a blue-plate special of a big break came on Thursday, during the lunch rush at Trolley’s Restaurant on 42nd Street between Eighth and Ninth avenues.

The four Anti Crime cops came in and sat down at their usual table just after noon.

Shortly after the hungry men ordered – two grilled chicken salads, one sandwich special and a roast-chicken platter – they noticed the handsome, brown-haired man.

But it wasn’t the Bensonhurst man’s natty clothes that caught their eyes.

The Russian immigrant was standing at the restaurant’s ATM, inserting blank card after card and withdrawing handfuls of money at a time, police sources said.

“The minute he stopped, they went after him and grabbed him at the door,” said Paul Vasiliadis, a Trolley’s employee.

“It was an awful surprise [for him] when they got to the door and grabbed him. He was pale white.”

Cops then rummaged through his bag and found stacks of $20 bills, Vasiliadis said.

He had 52 of the gray blank cards in the bag, along with $7,504 in cash.

With their lunches wrapped to go, the cops arrested Potupa and hauled him into nearby Midtown South station house – and quickly realized they’d stumbled onto something big.

“You’ve got to give them credit for being that observant,” said Vasiliadis. “It’s awesome. It’s a scam that hurts people and I’m glad they busted him.”

The U.S. Secret Service quickly swooped in and revealed they’d been tracking Potupa for a while in a joint probe with the FBI.

They pegged Potupa as a member of the international identity-theft ring and took over the investigation, the source said.

Potupa initially tried to say he’d found the cards and was just checking them out, the sources said.

Cops gave the cards a scan on an NYPD computer and saw they were actually clones of stolen cards – complete with legitimate users’ account information encoded on the magnetic strips, the sources said.

Faced with that incriminating information, Potupa changed his story and said he bought the cards online from a Canadian spammer.

A search of Potupa’s home revealed another 105 of the cards, almost $70,000 in cash, electronics, a money counter, jewelry, receipts and addresses of banks, the source said.

And an inspection of his 2006 gray Porsche – parked in a lot half a block away from the restaurant – revealed a stun gun and an additional $497, the source said.

“The guy was a good tipper, four or five bucks a shot,” the parking attendant remembered. “Of course, he’s got to tip, it’s a Porsche.”

The attendant said Potupa was a regular, and was shocked when cops came and impounded the car.

“He used to go and come back in an hour,” he said.

Cops also confiscated Potupa’s cellphone, which is rife with foreign phone numbers. Cops are working to trace those numbers.

Potupa broke down and confessed when he was shown the feds’ video, which captured him emptying an ATM, a source said.

Cops said he’s been hitting ATMs in diners, delis and bank branches with account information from unwitting victims, some as far away as the Midwest.

“Somehow, he’s managed to breach a security wall through computer wizardry,” said the source. “Or someone is selling him inside information.”

Potupa has been living like a high-roller with his alleged ill-gotten gains.

He liked to travel, drive fast cars and hang around with gorgeous women.

Recently, he traded his 2004 silver Porsche for a brand new 2006 Cayenne that cost him $69,000. It was confiscated by cops.

And DMV records show his license plate – POTUPA – was attached to a 2001 BMW and a 2004 BMW before he upgraded to the Porsches.

“One day [Potupa and his girlfriend] just started driving really fancy cars,” said a neighbor near his Bensonhurst apartment. “They drove around the fanciest cars in the neighborhood.”

Another neighbor, Ozhan Tastaban, 16, said, “I was wondering how he got all those nice cars. He just kept popping up with a new one.”

His tastes in women also veered toward the deluxe.

“He had such beautiful girlfriends,” said another neighbor, adding that he seemed completely trustworthy, bright and educated.

Neighbors believed he was a Russian-language TV journalist and his personal Web site shows photos of him in far-flung locales like Cambodia, Thailand and Turkey.

Among the hundreds of pictures are several of him with animals – holding a lizard, a turtle and a scorpion – and others of him wearing a Nazi helmet and leaning on an old U.S. jet fighter while in Vietnam.